This invention relates generally to medical instruments and, more particulary, to systems and methods for guiding medical instruments through a body or a portion of the body, such as a blood vessel.
Disease processes, e.g., tumors, inflammation of lymph nodes, and plaque build-up in arteries, often afflict the human body. To treat such disease, it often is necessary to insert a medical device into the body, and to guide the medical device to the diseased site. Once the medical device is adjacent the diseased site, the medical device typically is used to photoablate or otherwise remove or reduce the diseased tissue.
As one specific example, atherosclerotic plaque is known to build-up on the walls of arteries in the human body. Such plaque build-up restricts circulation and often causes cardiovascular problems, especially when the build-up occurs in coronary arteries. Accordingly, it is desirable to detect plaque build-up and remove or otherwise reduce such plaque build-up.
Known catheters implement laser energy to remove plaque build up on artery walls. One known catheter includes a laser source and a catheter body. The catheter body has a first end and a second end, or head, and several optical fibers extend between the first end and the second end. The laser source is coupled to each of the optical fibers adjacent the catheter body first end and is configured to transmit laser energy simultaneously through the optical fibers.
To remove arterial plaque, for example, the catheter body is positioned in the artery so that the second end of the catheter body is adjacent a region of plaque build-up. The laser source is then energized so that laser energy travels through each of the optical fibers and substantially photoablates the plaque adjacent the second end of the catheter body. The catheter body is then advanced through the region to photoablate the plaque in such region.
A guide wire typically is required to properly position the catheter in the artery. The guide wire is advanced through the artery and region of plaque build-up so that it forms a path through the artery and plaque build-up. The catheter is then guided through the artery using the guide wire.
One known catheter includes ultrasound sensors positioned at its distal end for displaying images of the artery while the catheter is advanced. Known ultrasound sensors are coupled to an outer perimeter of the catheter and emit sound waves substantially radially from the catheter distal end toward the artery wall. The sound waves then are reflected by the surrounding tissue, e.g., the artery wall and plaque, and toward the ultrasound sensors. The reflected sound waves are then compared to the transmitted sound waves to generate an ultrasound image of the tissue radially sounding the distal end.
To advance the catheter, an operator first positions the catheter at a first location in the artery. Sound waves are then emitted from and received by the ultrasound sensors, and an image is then displayed showing the artery tissue adjacent the circumference of the catheter at such first location. The catheter is then advanced to a second location in the artery, and a second image is displayed showing the artery at such location. This process is then continued until the catheter is advanced through the artery and the plaque-build up.
Utilizing known ultrasound sensors as described above results in displaying images of the portions of the arterial wall which are radially disposed about the catheter, but does not provide images of the arterial wall or plaque positioned immediately forward the catheter. Particularly, and because of the reflection of the sound waves, the sensors must be aligned within the artery so that the sound waves projected toward the artery wall are substantially perpendicular to the artery wall when reflected to the sensors. Sound waves that are not perpendicular to the artery wall may provide inaccurate signals, which may result in the display of inaccurate images, which is undesirable.
Inaccurate images may result in improperly guiding the catheter through the blood vessel, which is undesirable. Particularly, known catheters must be manually inserted and guided through the blood vessel. Typically, a surgeon or other operator utilizes the displayed images to guide the catheter through the vessel and avoid damaging healthy tissue, i.e., the artery wall. If an inaccurate image displays plaque even though such tissue actually is an artery wall, it is possible that the operator may photoablate the artery wall, which is undesirable.
It would be desirable to provide a guidance system which provides improved image accuracy as compared to known catheters. It also would be desirable for such guidance system to be substantially easy to implement in connection with medical apparatus other than catheters. It further would be desirable for such guidance system to facilitate automatic advancement of the catheter through the body.
These and other objects are attained by a catheter which, in one embodiment, includes a catheter body and at least one interferometric guidance system. The catheter body includes a bundle of optic fibers, each having a first end and a second end, and the second ends of the respective optic fibers form a substantially rounded catheter head.
Each interferometric guidance system is coupled to the catheter body and includes a first optic fiber, a second optic fiber, and a detecting element. The first optic fiber of each guidance system includes a first end and a second end, and is coupled to the catheter body so that the second end is adjacent the catheter head. The second optic fiber of each guidance system similarly includes a first end and a second end, and a reference mirror is positioned adjacent the second optic fiber second end.
The detecting element of each guidance system is communicatively coupled to both the first optic fiber and the second optic fiber of such guidance system. Particularly, the first optic fiber first end is communicatively coupled to the detecting element and the second optic fiber first end is communicatively coupled to the detecting element. The detecting element is configured to determine interference between substantially equal light beams which are emitted from the same source and which are split to propagate through the first optic fiber and through the second optic fiber. The interference is then utilized to determine the density and type of tissue adjacent the catheter head, and to guide the catheter head through the tissue.
In operation, the catheter head is inserted at least partially into a blood vessel so that the catheter head and the first optic fiber second end of each guidance system is positioned in the blood vessel. The second optic fiber of each guidance system is positioned outside the blood vessel. The reference mirror of each guidance system is positioned a desired, or measuring, distance from its respective second optic fiber second end. The distances between the respective reference mirrors and optic fiber second ends may either be the same or different.
With respect to each detecting element, a light beam is split into first and second substantially equal light beams which are then transmitted through the first and second optic fibers of each guidance system, from their respective first ends to their respective second ends. The first light beam transmitted through the first optic fiber exits from the first optic fiber second end, is at least partially reflected by the tissue, re-enters the first optic fiber second end and propagates toward the first optic fiber first end. Similarly, the second light beam transmitted through the second optic fiber exits from the second optic fiber second end, is at least partially reflected by the reference mirror, re-enters the second optic fiber second end and propagates toward the second optic fiber first end.
Each detecting element detects interference between the respective reflected first light beam and the reflected second light beam and transmits interference data to a computer. The computer then utilizes the interference data to determine the density and the type of the tissue to be examined adjacent the catheter head. Particularly, the interference data is representative of the density and type of tissue located at the measuring distance from the second optic fiber second end, and the computer utilizes such data to generate an image of such tissue at such location. The computer also utilizes the interference data to control subsequent advancement of the catheter through the artery.
The above described guidance systems facilitate obtaining more accurate images than obtained using ultrasound. In addition, such systems are believed to be substantially easy to implement in connection with medical apparatus other than catheters. Furthermore, such systems are believed to facilitate automatic control and advancement of the catheter through the body.